Compression release-type engine retarders are well-known in the art. Engine retarders are designed to temporarily convert an internal combustion engine of either the spark ignition or compression ignition type into an air compressor. The fundamental braking power is achieved by preventing fuel injection during the compression stroke of a piston, compressing the captured air mass, and releasing the compressed air at or near a top-dead-center position of a piston into an exhaust manifold. The energy expended in compression release braking systems is controlled, for the most part, by the volume of gas compressed, the timing of the release of the gas into the exhaust manifold and the amount of gas released. A compression release retarder decreases the kinetic energy of an engine by opposing the upward motion of the engine's pistons on the compression stroke. As a piston travels upward on its compression upstroke, the gases that are trapped in the cylinder are compressed. The compressed gases oppose the upward motion of the piston. When the piston nears the top of its stroke, an exhaust valve is opened to "release" the compressed gases. The pressure having been released from the cylinder, the piston cannot recapture the energy stored in the compressed gases on the subsequent expansion downstroke. In so doing, the engine develops retarding power to help slow down the vehicle. This provides the operator with increased control over the vehicle.
A properly designed and adjusted compression release-type engine retarder can develop retarding power that is a substantial portion of the power developed by the engine on positive power. Compression release-type retarders of this type supplement the braking capacity of the primary vehicle wheel braking system. In so doing, these retarders may substantially extend the life of the primary wheel braking system of the vehicle.
The basic design of a compression release type engine retarding system is disclosed in Cummins, U.S. Pat. No. 3,220,392. The compression release-type engine retarder disclosed in the Cummins patent employs a hydraulic system to control the operation of the exhaust valves to effect the compression release event. The hydraulic control system engages the engine's existing valve actuation system, namely, the rocker arms of the engine.
When the engine is operating under positive power, the hydraulic control system of the compression release retarder is disengaged from the valve control system, so that no compression release event occurs. When compression release retarding is desired, the engine is deprived of fuel and the hydraulic control system of the compression release brake engages the valve control system of the engine. The valve control system drives the compression release retarder to produce compression release events at the appropriate times.
The hydraulic systems of compression release engine retarders typically have a number of components. A master piston engages the valve control system of the engine, typically at a rocker arm. A solenoid valve is typically actuated to supply engine oil to fill the hydraulic circuits of the compression release engine retarder, when retarding is desired. The master piston, in turn, is hydraulically connected to a slave piston. The slave piston is connected to an exhaust valve of the engine.
When the compression release retarder is actuated, the rocker arm pushes against the master piston. The motion of the master piston forces the slave piston to actuate, which in turn opens the exhaust valve of the internal combustion engine at a point near the end of the compression stroke. Much of the energy stored by compressing the gas in the cylinder is not recovered during the subsequent expansion or power stroke of the engine. Instead, it is dissipated through the exhaust and radiator systems of the engine. By dissipating the energy developed by compressing the cylinder charge, the compression release-type retarder slows the vehicle down.
Typically, it is desired to open the compression release-type engine retarder as late in the engine cycle as possible. In this way, the engine develops greater compression, allowing more energy to be dissipated through the compression release retarder. Delaying the opening of the exhaust valve in the compression release event, however, may substantially increase the loading on critical engine components. The force required to open the exhaust valve during the compression release event is transmitted back through the hydraulic system through the push tubes and the camshaft. This can impose substantial force on certain engine components. If the timing is delayed long enough, the pressure in the cylinder can become high enough to exceed the ability of the compression release retarder to properly open the exhaust valve.
Historically, engine manufacturers desired to minimize modification of the engine. Consequently, compression release-type retarders originally were installed as after-market items. It was, therefore, necessary to design the compression release retarder to accept the existing rocker arm motion of the engine, without modification. A rocker arm that moves close to the desired time of the compression release event was typically selected as the initiating motion to effect the compression release event. A remote exhaust or intake rocker arm of another cylinder, that was undergoing either exhaust or intake at about the time of the desired compression release event, was frequently selected. In other cases, a fuel injector cam associated with a cylinder that was undergoing its compression event was selected. These design choices often required compromising performance to some degree.
Compression release retarders have enjoyed substantial and continuing commercial success in the marketplace. Engine manufacturers have been more willing to make engine design modifications to accommodate the compression release-type engine retarder, as well as to improve its performance and efficiency. Engine manufacturers are also increasingly willing to make other modifications to engine components that would enhance compression release retarding.
In the meantime, manufacturers continued to explore a variety of new ways to improve the efficiency of their engines. Environmental, safety, and efficiency demands have pushed the technology of compression release engine retarding significantly over the past 30 years. These changes have resulted in a number of engine modifications. As engines have become smaller and more fuel efficient, the demands on retarder performance have often increased, requiring the compression release-type engine retarder to generate greater amounts of retarding power under more stringent or limiting conditions.
Another method of engine retarding is exhaust braking, in which a restriction is imposed in the exhaust system. Exhaust braking systems expend a rolling vehicle's kinetic energy by temporarily restricting the exhaust flow through the exhaust system, thus causing the engine to expend greater energy pushing air from the cylinders during the normal exhaust stroke. The back pressure in the exhaust system is increased, making it harder for the piston to force gases out of the cylinder on the exhaust stroke.
The compression release-type retarder operates on the compression stroke of the engine, the exhaust-type retarder operates on the exhaust stroke. The exhaust restriction can be supplied by any of a number of means, all of which are well known in the art, for example, a butterfly or guillotine valve. With the exhaust restriction in place, the pressure of gases in the exhaust manifold rises. This, in turn, impairs the flow of gases out of the cylinder on the exhaust stroke. As the piston moves upward on the exhaust stroke, evacuating the cylinder, it is now pushing against a higher pressure in the manifold than when the gas restrictor was absent. This pressure pushes against the cylinder helping to slow the vehicle. In addition, the higher pressure in the exhaust manifold also means that not as much of the gases will be allowed to exit the cylinder on the exhaust stroke. This will leave a higher residual charge on the subsequent intake stroke than when an exhaust restriction was not being used. This higher residual cylinder charge will undergo compression. If a compression release-type retarder is also used in combination with the exhaust brake, the higher exhaust pressure can enhance the performance of the compression release-type retarder on the subsequent compression stroke.
Many engines also use a turbocharger to increase the amount of air forced into a cylinder on intake and improve performance. The use of an exhaust restrictor, however, inhibits turbocharger performance, dramatically reducing the amount of boost air delivered to the intake side of the engine. This effect dramatically impairs compression release-type engine brake performance.
As the market for compression release-type engine retarders has developed and matured, these multiple factors have pushed the direction of technological development toward a number of goals: securing higher retarding power from the compression release retarder; working with, in some cases, lower volumes and masses of air that are deliverable to the cylinders through the intake system; and the interrelationship (and sometimes interference) of various collateral or ancillary equipment, including: intake and/or exhaust silencer; turbocharger; and/or exhaust brake.
Engine manufacturers have also become increasingly willing to make design modifications to their engines that would increase the performance and reliability, and broaden the operating parameters, of compression release-type engine retarders. Various techniques to improve the efficiency of the engine on positive power have also been incorporated into engines. For example, a portion of the exhaust gases can be recirculated through the engine to attempt to achieve more complete burning of the exhaust gases, thereby reducing certain types of emissions. Various methods to increase the amount of exhaust gas delivered to the cylinder on intake have also been explored.
Exhaust gas recirculation systems are well known prior to the present invention. In most of these systems, however, a portion of the exhaust gas flow is diverted from a point downstream of the exhaust manifold to a point on the intake side of the engine during normal internal combustion operation of the engine. Although these technologies aid in controlling emissions, they require axillary hardware, such as piping and control systems. This in turn adds to the cost and complexity of the engine.
Ueno, Japanese Laid Open Patent No. Sho 63-25330 (February 1988), assigned to Isuzu, for Exhaust Brake Apparatus for Internal Combustion Engine, discloses a method of increasing the amount of gases delivered to the cylinder on intake. Ueno incorporates an additional lobe or bump on the cam that actuates an exhaust valve. Ueno incorporates an exhaust brake, which increases the pressure of exhaust gases in the exhaust manifold. The additional cam lobe forces the exhaust valve of the cylinder that will undergo the compression release retarding event to open near the end of its intake stroke. At this point, the pressure of gases in the cylinder on intake is low, relative to the pressure in the exhaust manifold. This opening causes additional gases to enter the low pressure cylinder on intake from the higher pressure exhaust manifold, increasing the amount of gases available to the compression release retarder on the succeeding compression stroke.
Neitz, et al., U.S. Pat. No. 4,981,119 (Jan. 1, 1991), for Method of Increasing the Exhaust Braking Power of an Internal Combustion Engine, discloses a method in which an exhaust valve is opened briefly at the end of the intake stroke to increase the air charge to the cylinder. This increases the retarding power realized from a compression release event. The Neitz method is also carried out in combination with exhaust braking.
Gobert, et al., U.S. Pat. No. 5,146,890 (Sep. 15, 1992). for Method and a Device for Engine Braking of a Four-Stroke Internal Combustion Engine, discloses yet another method for controlling the actuation of the exhaust valve at the end of the intake and beginning of the compression stroke. To increase the amount of gases trapped in the cylinder on compression, communication is established between the combustion chamber and the exhaust system when the piston is located in the proximity of its bottom-dead-center position after the inlet stroke.
None of these methods, however, provide solutions to certain problems of compression release-type retarding. They each suffer, at least three fundamental limitations. First, all of these prior methods require modification of the engine cam profile, which is not feasible. It would be desirable, therefore, to have a system for accomplishing exhaust gas recirculation on compression release retarding and exhaust gas recirculation on positive power that does not require modifying the cam profile. Furthermore, it is desirable to have a system that does not require any modification of the valve train kinematics.
Prior systems, however, use an extra lobe. This requires running the compression release retarder with extra lash built into the retarder setting. Although numerous systems exist for absorbing this extra lash, they are complex hydraulic systems that typically require additional parts for either the compression released retarder or the engine. It is, therefore, desirable to maintain the existing cam profile of the engine as manufactured, without the use of any extra lobes, extra lash, or additional parts to either the compression release-type retarder or the engine. The present inventors believe that doing so will enhance the reliability of the compression release retarder and the exhaust gas recirculation system.
Second, none of these prior systems disclose, teach, or suggest how to optimize the actuation of the exhaust valve during the intake and compression strokes to achieve the highest possible retarding power from the compression release event, without exceeding the mechanical limits of the engine. Prior systems typically involve unusual dynamic or kinematic loads.
Third, compression release retarders are typically optimized and set for a rated power. The engine, however, is not always operated at its rated speed and is frequently operated at lower speeds. The advertised retarding performance based on the rated speed cannot typically be achieved when operating at lower speeds. It is, therefore, desirable to provide a method for controlling the braking systems and better tuning them to the speed at which the engine is operating. This is not possible with prior methods, including those discussed above.
There remains a significant need for a method for controlling the actuation of the exhaust valve to increase the effectiveness of and to optimize the compression release retarding event. There is a significant need for a system that is able to perform that function over a wide range of engine operating parameters and conditions. In particular, there remains a need to "tune" the compression release-type retarder system to optimize its performance at lower operating speeds than the rated speed of the device.
Relatively large forces must be applied to open the exhaust valves on compression. All of the known systems for supplying the necessary power to open exhaust valves for exhaust gas recirculation and/or compression release braking derive the necessary power from components of the engine that are actuated on a fixed engine timing. Currently, solenoid switches are not capable of producing the necessary forces. Even if this were possible, it is likely that these switches would be unacceptably large and too expensive to be viable for use in a compression release retarder. As discussed above, known hydraulic systems are not able to open the valves to optimize the compression release retarding over a range of engine speeds.
Because the motion used to initiate a compression release event is derived from a contemporaneously moving engine component, hydraulic systems have typically looked to a point on the engine physically remote from the exhaust valve to be opened to derive energy to actuate a compression release event. For example, it may be that the only rocker arm moving at the correct time to open the exhaust valve is on another bank of the engine, or at the other end of the engine block. The length of the hydraulic circuit (with its associated hydraulic compliance) could preclude use of that energy. If, instead, another component is chosen, located closer to the exhaust valve of interest, it may be moving at a time that is not practicable for either compression release or exhaust gas recirculation valve actuation.
Although the Assignee of the present application is also the owner of a number of prior patents for systems that can modify the derived motion, none of these systems provide sufficient control over a range of engine speed to overcome these problems: Meistrick, U.S. Pat. No. 4,706,625 (Nov. 17, 1987) for Engine Retarder With Reset Auto-Lash Mechanism; Hu, U.S. Pat. No. 5,161,501 (Nov. 10, 1992) for Self-Clipping Slave Piston; Custer, U.S. Pat. No. 5,186,141 (Feb. 16, 1993) for Engine Brake Timing Control Mechanism; Hu, U.S. Pat. No. 5,201,290 (Apr. 13, 1993) for Compression Relief Engine Retarder Clip Valve; Meistrick, U.S. Pat. No. 4,949,751 for Compression Release Retarder with Valve Motion Modifier; and Joko, U.S. Pat. Nos. 5,406,918 and 5,485,819 for Internal Combustion Engine, all of which are incorporated herein by reference.
While valve lash adjustment systems for advancing the time of valve opening are known prior to the present invention, such systems are limited to: (i) making the valve open earlier, close later, and increasing lift; or (ii) making the valve open later, close earlier, and decreasing lift. These lash adjustment systems do not enable independent control of the time at which a valve is opened and/or closed, or of the lift of the valve. Applicants believe these factors are beneficial to obtain optimal valve opening for exhaust gas and/or gas recirculation and compression release braking. Furthermore, the prior art lash adjustment systems may also not be easily adjusted (or adjustable at all) while the engine is operating. This ease of adjustment is desirable, to change the timing of valve opening, closing, and lift during engine operation to optimize engine breaking over a range of engine speeds.
The present invention, on the other hand, provides a number of benefits that are not available with known prior devices in systems. First, the present invention achieves increased trapped charge to the cylinder at about bottom dead center of the intake stroke. This charge is retained during the subsequent compression stroke resulting in enhanced compression released retarding. Second, the passage for exhaust gas is substantially shorter in the present invention than in systems that recirculate the exhaust gas through the intake portion of the engine. Recirculation in the present invention is accomplished from the exhaust manifold directly into the cylinder, rather than through a separate recirculation circuit. This results in increased fuel efficiency and improved emission control. Others have done this, as noted above. Moreover, exhaust gas recirculation has not commonly been employed in diesel engines prior to the present invention. The present inventors believe that the invention overcomes a number of the obstacles or problems that were unresolved by the prior methods and systems.